N.K. Tyuleneva

Inhibited oxidation of a polyethylene melt

Abstract The oxidation of linear polyethylene inhibited by an effective antioxidant of the phenolic type, viz. 2,2′-methylene-bis (4-methyl-6-tert. butylphenol), has been studied over the temperature range 170–210. There is a critical concentration of antioxidant above which the rate of its consumption is directly proportional to its concentration. Deviations from this dependence are due to chain initiation by direct oxidation of the polymer and to reactions involving the products derived from the antioxidant: these products can also retard the oxidation. Similar results have been obtained using the amine type antioxidant, N-phenyl-N′-cyclohexyl-p-phenylenediamine. Some features of the mechanism of polyolefin oxidation are discussed.

Inhibited oxidation of polyethylene: anatomy of induction period☆

Abstract Oxidation of high-density polyethylene containing the strong phenolic antioxidant 2,2′-methylene-bis(4-methyl-6-tertbutylphenol) has been studied. During the induction period the antioxidant is consumed according to first-order kinetics, the rate constant depending on the initial antioxidant concentration; during the induction period about three moles of O 2 are consumed per mole of antioxidant. Formation of hydrogen peroxide in the induction period of oxidation has been established. The mechanism of inhibited oxidation is discussed. Antioxidants are more reactive compounds than polymers as such and, on being added to a polymer, they participate in many processes proceeding in it. Although the most important of these processes is chain termination, the major part of the antioxidant is usually consumed in direct reaction with oxygen and in termination of secondary chains initiated by its oxidation. In this work we studied some regularities of consumption of a strong antioxidant 2,2′- methylene-bis(4-methyl-6-tert,butylphenol) (MBP) in oxidation of high-density polyethylene.

Interaction of a phenolic antioxidant dissolved in polycarbonate with molecular oxygen

Abstract The reaction of the antioxidant 2,2′-methylene-bis(4-methyl-6-tertbutylphenol), dissolved in polycarbonate, with O 2 has been studied at 200 °C and oxygen pressure 300 mm Hg. The reaction follows first-order kinetics related to antioxidant concentration; its rate is directly proportional to oxygen pressure. The apparent rate constant is 1.1 × 10 −4 s −1 , or 3.7 × 10 −7 s −1 mm Hg −1 . The process is complicated with oxidation of the intermediate product, presumably monophenol X. The rate constant of its oxidation is about 1.6 × 10 −4 s −1 or 5.5 × 10 −7 s −1 mm Hg −1 . Peroxides were found among the volatile oxidation products.

Oxidation of an unevenly inhibited polymer

Abstract The oxidation of an atactic polypropylene sample containing an inhibitor follows one of two possible paths if the inhibitor is absent from a part of the sample. If the non-inhibited part is smaller than a certain limit, the inhibitor diffuses into this part and hinders oxidation. If it is larger, a stable zone of fast oxidation expanding with time is created in this part. The dependence of the limiting size of the non-inhibited zone on temperature and on the inhibitor concentration beyond the zone boundaries was studied experimentally.

Evaluation of antioxidant effectiveness in polyolefins

Abstract Antioxidants added to a polymer take part not only in reactions leading to retardation of the polymer oxidation, but also in many other stages of the oxidation process, including direct interaction with oxygen. Their effectiveness in polyolefins can be evaluated by analysing the dependence of oxygen consumption rate on initial antioxidant concentration.

Oxidation of polyethylene stabilized by a strong phenolic antioxidant

The law of consumption of the strong phenolic antioxidant in polyethylene oxidized is close to first order for the antioxidant and oxygen; the effective rate constant of consumption of the antioxidant and its critical concentration conform to the Arrhenius law. Slight deviations were detected from the first order rule both for the antioxidant and oxygen. The rate constant of consumption of the antioxidant decreases in the presence of a hydroperoxide reducing agent (synergist). Polymer molecular weight varies slightly during the induction period. Some problems of the inhibited oxidation mechanism of polyethylene were discussed.

Processes occurring in the period of induction of inhibited oxidation of polyethylene

The kinetics of oxygen uptake during the period of induction of inhibited oxidation of high-density polyethylene (melt) at 180–220°C and an oxygen pressure 300 mm Hg has been studied. The kinetic curves of consumption of O2 have a complex form and the rate of oxygen-uptake with rise in the concentration of the inhibitor 2,2′-methylene-bis-4-methyl-6-tert-butyl-phenol passes through a minimum. The molecular weight distribution narrows in the course of oxidation through loss of the highest molecular weight fractions. Analysis of the patterns found permits separate determination of the rate of oxygen uptake by polymer and inhibitor.

Development of an oxidation reaction in a nonuniformly inhibited polymer

1. The theory of the development of a chain reaction in a nonuniformly inhibited sample, considering quadratic termination, was discussed. 2. The appearance of a front of the oxidation reaction, propagated from the originally nonionized portion into the inhibited portion of the sample, was demonstrated by calculation on an electronic computer and experimentally.

Inhibited oxidation of polyethylene : Anatomy of induction period

Abstract Oxidation of high-density polyethylene containing strong phenolic antioxidant 2,2′-methylene-bis(4-methyl-6-tertbutyl-phenol) has been studied. During the induction period the antioxidant is consumed according to first kinetical order with the rate constant depending on the initial antioxidant concentration. During the induction period about three moles of O2 are consumed per one mole of antioxidant. The formation of hydrogen peroxide in induction period of oxidation has been established. The mechanism of inhibited oxidation is discussed.